Historically, exudate from a wound has been treated by absorbing it using a dressing containing an absorbent material. Such dressings have contained a padded absorbent material attached to an adhesive tape backing. The padded absorbent material is applied to the wound to absorb the wound exudate. A difficulty with this type of dressing is that the scab typically forms in and as part of the pad as the wound heals. Thus, when the dressing is removed, the scab is removed. This problem has been addressed by providing a porous film between the absorbent material and the wound to reduce the likelihood that a scab formed will become attached to the absorbent material
Some current wound care products use a hydrocolloid absorbent. Such materials typically have poor transparency so the treatment state cannot be observed from the outside. Also, such a material can partially lose its integrity after absorbing wound fluid. Flexibility of hydrocolloid dressings can be poor, which makes it difficult to apply the dressing to a bend portion of a body, such as a joint, etc. The portion of the absorbent in contact with the wound is converted to a gel-like material, and, when the dressing is removed, a portion of this absorbent material can be left in the wound, and must be removed to permit examination and/or before applying another dressing.
More recently the use of so-called “occlusive” dressings for pressure sores and ulcers has gained acceptance. Most of these products are formed from several layers, including at least an inner skin-contacting layer and an outer backing layer. The dressing is applied as a cover for the sore or ulcer in a size providing a margin around the wound area that adhesively seals to the skin. An inner layer contains water-absorptive materials, so that fluid from the wound is absorbed into the layer, making it possible to keep the dressing in place for at least several days. Such occlusive dressings tend to promote healing by maintaining the wound under moist conditions without forming a crust, and serving as a barrier against bacterial infection. Such dressings for “moist wound healing” are particularly useful for dermal burns, traumatic skin deficiencies, incised wounds, and the like.
The chemistry of acetoacetate compounds, and the Michael addition to acrylates has been described. For example, Mozner and Rheinberger reported the Michael addition of acetoacetates having a β-dicarbonyl group to triacrylates and tetracrylates to form gel products. See Macromolecular Rapid Communications 16 135-138 (1995).
U.S. Pat. No. 6,025,410 notes that the stoichiometry of the Michael donor to the Michael acceptor is critical to controlling the molecular weight. The reference teaches that certain soluble liquid uncrosslinked oligomers, made by one step Michael addition of acetoacetates to multi-acrylates, can be further crosslinked using ultraviolet light without using photoinitiators. If proportions below the claimed ranges are used, crosslinked gels or solid products are made which are not useful because only un-gelled, uncrosslinked liquid oligomers will further crosslink without adding photoinitiators. The described liquid oligomer compositions, since they are liquids, can readily be applied to various substrates using conventional coating techniques such as roll or spray prior to ultraviolet light cure.
U.S. Pat. No. 5,132,367 describes NCO-free resins and cured products thereof. The cured products are obtained by a Michael reaction of an acetoacetylated (meth)acrylic resin or an acetoacetylated polyester and an NCO-free polyurethane having at least two (meth)acrylic end groups. U.S. Pat. No. 5,132,367 however does not teach the use of these products in electrical applications.
EP 227454 discloses a process for preparing a cured polymer involving the Michael reaction of an acetoacetylated polyol and a poly α,β-unsaturated ester. The obtained cured products are said to exhibit excellent adhesion, excellent solvent resistance, excellent gloss retention, good flexibility and hardness.
U.S. Pat. No. 5,459,178 describes mixtures comprising an acetoacetate ester, an α,β-ethylenically unsaturated monomer and a liquid tertiary amine catalyst. A cured system is obtained by reacting these components. The acetoacetate ester used is prepared by transesterification of polyhydroxyl compound having an average of at least two hydroxy groups with an alkylacetoacetate.
U.S. Pat. No. 4,871,822 discloses a Michael reaction of olefinically unsaturated compounds with compounds containing at least two active hydrogen atoms for 2 component lacquers. As olefinically unsaturated compounds there are considered compounds having at least two α,β-unsaturated carbonyl groups. There are a large number of Michael donors including acetoacetylated polyols or polyamines and such compounds as e.g. acetylacetone or benzoylacetone.
David L. Trumbo in Polymer Bulletin 26, pages 265-270 (1991) discloses Michael addition polymers obtained from 1,4- and 1,3-benzenedimethanol diacetoacetates and tripropylene glycol diacrylate. The reference describes that in case the reactants are used in stoichometric amounts of the reactive groups, gelation of the system is observed. In another paper (Polymer Bulletin 26, pages 481-485 (1991)) the same author described Michael addition polymers obtained from the reaction of a bis(acetoacetyl) amide or an aliphatic acetoacetate and a di-acrylate comonomer. However, no utilisation or properties of the polymers are described in these articles.
WO 95/16749 describes a water-borne curable composition that comprises an acetoacetylated polymer in the form of an aqueous solution, dispersion or emulsion and a polyacrylate that has at least two (meth)acrylate end groups. According to this publication, such composition is stable even in the presence of a catalyst until the water is evaporated from the system.
The use of acetoacetyl chemistry, in particular the use of acetoacetylated resin, in thermosetting systems is further described in Journal of Coatings Technology Vol. 61 no. 771 page 31 to 37; Journal of Coatings Technology Vol. 65 no. 821 page 63 to 69; Surface Coatings Australia, September 1989 page 6 to 15; and Journal of Coatings Technology Vol. 61 no. 770 page 83 to 91.
U.S. Pat. No. 4,408,018 describes a method for effecting the cross linking of polymers comprises (a) introducing a plurality of pendant acetoacetate moieties into an acrylate polymer backbone; (b) mixing the polymer with (i) a crosslinking agent having at least two groups and (ii) a strong base catalyst effective to initiate a Michael reaction, and (c) effecting reaction between the pendant acetoacetate moieties and the polyacrylate. The polyacrylate containing pendant acetoacetate groups is made e.g. by copolymerising the acetoacetic ester of hydroxyethyl(meth)acrylate with the monomers forming the acrylate polymer. The polyacrylate cross linker is e.g. trimethylol propane triacrylate (I). The polyacrylate resin is esp. a styrene-acrylate copolymer contg. pendant acetoacetate gps.